Field of the Invention
The invention relates to a coated method for the preparation of a separator comprising multiple layers of glass or glass and ceramic particles for use in an electrochemical cell, an electrochemical cell comprising such a separator and the use of such an electrochemical cell.
Brief Description of the Related Art
Beyond consumer electronics, Li-ion batteries are growing in popularity for stationary applications as storage of renewable energy, grid levelling, solar, large hybrid diesel engines, military, hybrid electric vehicles (HEV-s), and aerospace applications due to their high energy density.
A separator is a critical component within an electrochemical cell, especially for safety issues and life time. The separator absorbs the electrolyte so that it is filled with the electrolyte. It thereby allows the ionic conduction through the liquid electrolyte while keeping the positive and negative electrode separate. In order to improve the electrochemical cell's performance the used separator has to fulfil various requirements: mechanical stability, high thermal stability, zero shrinkage, porosity, in some instances ionic conductivity, etc. The quality of the separator will influence the characteristics of the separator electrochemical cell interface, internal resistance, and effectively influence the electrochemical cell's capacity, charge/discharge cycling capabilities, charge/discharge current density, and various electrical properties.
For large-scale (high energy and high power) electrochemical cells, safety issues are a critical challenge and for this reason the electrochemical cell manufacturers focus on improving manufacturing methods and increasing safety. Nowadays, the demand for high energy and high power electrochemical cells is rising rapidly. To generate such high current capacity and current density without disrupting the high-voltage capability, the separator must be mechanically stable and possess higher porosity than those in traditional batteries for consumer applications. Furthermore, the separator must be thermally stable at high temperatures in order to produce a stable, high-powered electrochemical cell.
Separators of the state of the art are usually single layer or multilayer polyolefin based separators. Alternatively, the separator may be produced with direct coating of ceramic particles with a binder polymer on the surface of the porous substrate.
Ceramic and/or glass particles may also be coated directly on the electrode surface, as for example disclosed in WO 2005/076388.
Commercially available polyolefin separators do not readily absorb the electrolyte solvents with high dielectric constants, such as ethylene carbonate (EC), and propylene carbonate (PC), because of their hydrophobic surfaces with low surface energy, and they have poor ability to retain the electrolyte solutions. In addition, the solvent leakage from the interfaces between the electrodes or the opposite sides of current collectors often causes the deterioration of the cycle life of electrochemical cells. Conventional separators of the state of the art usually shrink during heat generation.
U.S. Pat. No. 8,216,722 discloses a battery comprising a separator which in turn comprises a first, second and possibly third phase intermixed with one another, wherein the second phase comprises ionically conductive particles, such as ceramic particles, glass particles, glass-ceramic particles, and mixtures thereof. There is only one layer of the separator and the separator is substantially non-porous and solid-state.